Successfully complete Tails' driving quest in the Hero side story to unlock the kart racing mini-game in the Hero side story. Successfully complete Rouge's chase mission in the Dark side story to unlock the kart racing mini-game in the Dark side story.

Boss attack mode

Successfully complete the Hero or Dark side story modes to unlock boss attack mode. You will be able to fight the bosses from the side of the story you completed.

Last stage

Successfully complete the Hero and Dark side story modes. Then, enter story mode and a "Last Stage?" selection will appear on the menu between the Hero and Dark selections.

Bonus stage

To get a 3D version of the Green Hills Zone stage, from Sonic The Hedgehog, you must get all the Emblems, including Kart, Timed Boss, and the emblems for all "A" rating. Once you have them all, which should total 180, the island next to the Green Forest stage will have the face of Sonic on it.

Play as Sonic in alternate costume in Kart mode

Successfully complete all of Sonic's stages and missions to unlock him in the PSO suit in Kart mode.

Play as Shadow in alternate costume in Kart mode

Successfully complete all of Shadow's stages and missions to unlock him in an alternate costume in Kart mode.

Play as Tails in the Tornado 1 in Kart mode

Successfully complete all of Tails' stages and missions to unlock him in the Tornado 1 in Kart mode.

Play as Eggman in alternate Eggwalker in Kart mode

Successfully complete all of Eggman's stages and missions to unlock him in his alternate Eggwalker in Kart mode.

Play as Knuckles in alternate form in Kart mode

Successfully complete all of Knuckles' stages and missions to unlock him in his alternate form in Kart mode.

Play as Rouge in alternate costume in Kart mode

Successfully complete all of Rouge's stages and missions to unlock her in an alternate costume in Kart mode.

Play as Amy Rose in Kart mode

Successfully complete all of Sonic's stages and missions with an "A" ranking to unlock Amy Rose in Kart mode.

Play as Metal Sonic in Kart mode

Successfully complete all of Shadow's stages and missions with an "A" ranking to unlock Metal Sonic in Kart mode.

Play as Tikal The Echinda in Kart mode

Successfully complete all of Knuckles' stages and missions with an "A" ranking to unlock Tikal The Echinda in Kart mode.

Multiplayer characters

Collect all 180 Emblems to unlock the following hidden multiplayer characters:

At the start of the City Escape stage, instead of landing on the ground with the board, scrape the roads on the board. When on foot run full speed at a wall and get knocked down. Pause the game if you fall after hitting the wall. Choose to restart the stage to run on foot and not on the board.

Quickly complete Security Hall stage

In the Security Hall stage you play as Rouge The Bat and are given 5 minutes to complete it. This can be quite difficult. If you have enough lives you can do this trick. If you cannot seem to find the Emeralds, intentionally die. You will keep the existing Emeralds that you have collected. You will begin at the start of the level and the Emeralds will move to different places. This is the fastest method for completing the stage if you are having trouble.

Big The Cat appearances

In Knuckles' Pumpkin Hill stage, go to the one of the train gates. You can see Big The Cat hiding behind the gate, waving to you. In the City Escape stage, Big The Cat appears after the last corner in the G.U.N. truck vs. Sonic scene. Look for him at the right of the screen, running downhill on the sidewalk away from the truck. In the Tails stage where you are running from the police and you first get your hover ability, Big The Cat can be seen again. There is a part in the level where you need to knock a column over in order to use it as a step to reach a higher level, from which you hover over to a platform with a police barricade and two robots. If you miss the platform and fall in the hole, you will see Big the Cat sitting on the girders underneath the platform. You can also see him in the battle against Sonic while playing as Shadow.

E102 appearance

In Rouge's Inside the Pyramid stage, one of the robots you blow up is E-102.

Achievements

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Hello World (20 points): Hello, rookie, welcome to the Sonic World!

Chao! (20 points): Welcome to the Chao World!

Chao Raiser (20 points): Time to raise your Chao.

HERO! (20 points): You have cleared our HERO story.

DARK! (20 points): You have cleared our DARK story.

Boss Attack (20 points): Your skill is top notch!

Mission Complete (20 points): Now you are the master of this stage.

Heaven or Hell (40 points): You have successfully unlocked the HERO and DARK gardens.

Beyond Good And Evil (40 points): My hero, you have successfully saved the world!

Speedy Racer (40 points): Excellent driving skills!

Emblem Collector (40 points): Half way to go!

You Are The Legend (100 points): You are the Sonic expert now!

The following achievements require the "Battle Mode" bonus downloadable content: